An antithrombin-III (hereinafter referred to as AT-III) is a kind of sugar protein belonging to .alpha..sub.2 globulin present in plasma and has a molecular weight of 65,000-68,000. An AT-III has a protease inhibitory activity and shows a strong inhibitory action on coagulation activity of thrombin, as well as an inhibitory action on other blood coagulation factors, activated X factor, activated IX factor and the like. It has been reported that AT-III also shows an inhibitory action on plasmin and trypsin. These inhibitory actions are known to generally proceed faster in the presence of heparin.
An AT-III having such pharmacological actions is used for the correction of abnormally enhanced coagulation, specifically for the treatment of disseminated intravascular coagulation (DIC). AT-III shows poor stability when dissolved and causes side effects in intravenous administration by polymerizing. Accordingly, AT-III has been formulated into lyophilized preparations.
Incidentally, liquid preparations are more advantageous than lyophilized preparations in that they do not require dissolution in injectable distilled water when in use, thus making administration easy, and are produced economically with no need for a freeze-dry step in the production thereof. However, practical formulation of AT-III into liquid preparations has gotten behind due to the poor stability of AT-III in a solution state. There has been only one report in the field of reagent that confirms possible 7 day storage of AT-III in a solution state at 4.degree. C. in the presence of heparin (Japanese Patent Unexamined Publication No. 103463/1980).